The coordination chemistry of two symmetric double-armed oxadiazole-bridged organic ligands with copper salts

Two new symmetric double-armed oxadiazole-bridged ligands, 4-methyl-{5-[5-methyl-2-(pyridin-3-ylcarbonyloxy) phenyl]-1,3,4-oxadiazol-2-yl}phenyl pyridine-3-carboxylate (L1) and 4-methyl-{5-[5-methyl-2-(pyridin-4-ylcarbonyloxy)phenyl]-1,3,4-oxadiazol-2-yl} phenyl pyridine-4-carboxylate (L2), were prepared by the reaction of 2,5-bis(2-hydroxy-5-methylphenyl)-1,3,4-oxadiazole with nicotinoyl chloride and isonicotinoyl chloride, respectively. Ligand L1 can be used as an organic clip to bind Cu-II cations and generate a molecular complex, bis(4-methyl-{5-[5-methyl-2-(pyridin-3-ylcarbonyloxy)phenyl]-1,3,4-oxadiazol-2-yl}phenyl pyridine-3-carboxylate) bis(perchlorato)copper(II), [Cu(ClO4)(2)(C28H20N4O5)(2)], (I). In compound (I), the Cu-II cation is located on an inversion centre and is hexacoordinated in a distorted octahedral geometry, with the pyridine N atoms of two L1 ligands in the equatorial positions and two weakly coordinating perchlorate counter-ions in the axial positions. The two arms of the L1 ligands bend inward and converge at the Cu-II coordination point to give rise to a spirometallocycle. Ligand L2 binds Cu-I cations to generate a supramolecule, diacetonitriledi-mu(3)-iodido-di-mu(2)-iodido-bis(4-methyl-{5-[5-methyl-2-(pyridin-4-ylcarbonyloxy)phenyl]-1,3,4-oxadiazol-2-yl}phenyl pyridine-4-carboxylate)tetracopper(I), [Cu4I4(CH3CN)(2)(C28H20N4O5)(2)], (II). The asymmetric unit of (II) indicates that it contains two Cu-I atoms, one L2 ligand, one acetonitrile ligand and two iodide ligands. Both of the Cu-I atoms are four-coordinated in an approximately tetrahedral environment. The molecule is centrosymmetric and the four I atoms and four Cu-I atoms form a rope-ladder-type [Cu4I4] unit. Discrete units are linked into one-dimensional chains through pi-pi interactions.